Devices suitable for delivering very small volumes of fluid have been available for several decades. Osmotic pumps are of particular interest for delivering small amounts of drugs or other similar applications. These osmotic pumps typically utilize a driving force based on a concentration gradient across a semi-permeable membrane. Most current designs involve a variety of flexible housings and may include one or more chambers. Unfortunately, these pumps tend to have limited control over the flow rate. Specifically, the flexible housings and membranes can create fluctuations in flow rate which are unpredictable. Although this may be acceptable in some applications, fluctuations in flow rate can generally be unacceptable for applications requiring more precise flow rates. In addition, any changes in contours or surface area of the semi-permeable membrane can affect the flow rate of solvent across the membrane.
Furthermore, continuous precise delivery of fluids for extended periods of time can present a unique challenge to these types of devices. Most often, current technologies are limited to delivery times of several weeks to a couple of months. If used in a patient, this requires frequent replacement and can be inconvenient. Further, such short useful durations increase costs associated with replacement, maintenance, and materials.
As such, cost effective systems and devices that are capable of effectively delivering relatively small volumes of fluids over an extended period of time continue to be sought through ongoing research and development efforts.